1. Technical Field
The present invention relates to a test apparatus and a device for calibration. More particularly, the present invention relates to a test apparatus that can adjust skews between drivers or between comparators.
2. Related Art
As a test apparatus for testing a device under test such as a semiconductor circuit, an apparatus including a plurality of drivers and a plurality of comparators is known. The plurality of drivers are circuits that input test signals into a plurality of input terminals of the device under test, and the plurality of comparators are circuits that measure measured signals from a plurality of output terminals of the device under test.
When providing the test signals to the plurality of input pins of the device under test to test the device, it is preferable that the test signals are input into the plurality of input pins at the same time or with a predetermined timing difference. Moreover, when measuring the measured signals from the plurality of output pins of the device under test, it is preferable that the measured signals are input into the plurality of comparators at the same time or with a predetermined timing difference.
However, the plurality of test signals or the plurality of measured signals has an indeterminate skew due to fluctuation of output timings of test signals in the plurality of drivers, delay amounts of transmission routes, sampling timings in the plurality of comparators, and so on. For this reason, it is preferable to measure this skew before testing the device under test and previously perform calibration compensating for the skew.
As a technique for measuring skews between plural signals, there is considered a technique for statistically measuring skews by means of a time interval analyzer, a frequency counter, or the like. For example, there is known a technique for measuring timing differences at a zero crossing point of measured signals by means of a time interval analyzer and measuring skews on the basis of a distribution of the timing differences (for example, see “Jitter Analysis Clock Solutions”, Wavecrest Corp., 1998).
Moreover, a technique for computing an instantaneous phase from an analytic signal of a measured signal and computing a skew from an initial phase difference of the instantaneous phase is proposed as disclosed, for example, in U.S. Pat. No. 7,127,018.
However, a technique using a time interval analyzer or the like has a dead time for which measurement cannot be performed from measuring a timing at one zero crossing point to measuring a timing at the next zero crossing point. For this reason, measuring data necessary for acquiring sufficient measurement accuracy extremely requires time.
Moreover, in a technique using an analytic signal, the analytic signal is computed from a result obtained by sampling a measured signal. At this time, it is preferable to use an A/D converter having about eight-bit resolution in an amplitude direction in order to compute the analytic signal with high precision. However, in the case of a measurement pin of a semiconductor testing apparatus or the like, it is difficult to measure a skew with high accuracy because a one-bit comparator samples a measured signal in order to detect a logical value of the measured signal.